The vast majority of cocaine abusers, including those enrolled in drug abuse treatment, regularly use and abuse other drugs. Unfortunately, little scientific information is available regarding how such other drug use influences the probability of cocaine use. The purpose of this project is to conduct controlled laboratory experiments in experienced cocaine users examining how pretreatment with other drugs influences the probability of cocaine use. During the past year a study examining the influence of acutely administered alcohol on cocaine use was completed and a study on caffeine begun. Alcohol significantly increased cocaine use, while preliminary data with caffeine suggests it does not alter preference for cocaine. We also completed an experiment demonstrating that acute cocaine use increases rates of cigarette smoking. We plan to complete the caffeine study and initiate a study examining the influence of smoked marijuana on cocaine use during the next year. Data collection in alcohol study has been published. The caffeine study is complete and in preparation for publication.